98 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 8,
of the fact of all but one of the 19 peculiar and mostly exclusively
Arctic forms of Bridlington being absent from the Lower and Middle
Glacial, that of these 72 forms no less than 46 do not occur at
Bridlington; and even yet more striking is it that, of this 46, only
1 is exclusively Arctic.
I may add that the difference in latitude between Bridlington and these Lower and Middle Glacial shell-localities does not exceed one degree*, and that the actual distance between them and Bridlington is from 100 to 120 miles.
I defer any remarks upon the striking, Crag-like, and seemingly southern facies of the Middle-Glacial fauna, because I expect to add materially to the number of that fauna, and because it will be more advantageously considered when describing the structure of the Lower and Middle Glacial formations.
We see however, that, as the evidence at present stands, the fauna yet obtained from the Lower and Middle Glacial deposits (especially that from the latter) presents almost as much dissimilarity to the Bridlington fauna as the mollusca of the German Ocean do to those of the Greenland and Spitzbergen seas; so that no grounds exist for identifying, upon palaeontological evidence, those Glacial beds of the Eastern Counties which are inferior to the great chalky clay, and whose structure and physical relationship to the Crag we have the advantage of studying in immediate contiguity to the Crag itself, with any of the Glacial series of Yorkshire, but, on the contrary, that the palaeontological evidence points to their complete distinction. The uppermost of the East-Anglian series, the great chalky clay, with which Mr. Rome and myself identified the basement-clay of Holderness (a), has never yielded any other than derivative fossils; but this basement clay at Dimlington cliff, teeming with chalk (a), has, near to its junction with the base of the purple clay (c), lately yielded Sir Charles Lyell a few forms of mollusca which, he informs me, he regards, as far as they go, as resembling those of the Bridlington bed. The position of the base of Dimlington cliff, whence Sir Charles obtained these, is indicated, according to my view of the case, in the vertical section, the basement-clay from which these shells came appearing, from adjacent borings, to descend upwards of 100 feet below the base of the cliff.
I now propose to examine, on physical grounds, what part of the Yorkshire clay may, and what may not, be regarded as identical with the uppermost or great chalky member of the East-Anglian series.
The absence of chalk debris in the clay lying to the north of the Wolds seems to have been regarded by geologists as evidence of a drift from north to south, though the hypothesis never appears to have been brought to the test of critical examination until Mr. Borne and I, in our quoted paper, cursorily endeavoured to refute it. Nor do geologists ever appear to have noticed the fact, so con-
- In the case, however, of one shell, Ostrea edulis, obtained only at Stevenage,
the difference in the latitude is nearly two degrees.
